The Periodic Table

The Periodic Table is the central tool of the chemist, but it is used by scientists in all fields of study. It was developed by Russian Scientist, Dmitri Mendeleev, in the 1800s. The more modern version of the table is credited to Henry Mosely.

The Periodic Table The periodic table is essentially a list of known elements. It gives information about each element and for that reason it is a very valuable tool.

Arrangement of the Periodic Table The horizontal rows (periods) represent a series of elements with increasing weight and changing properties.

Arrangement of the Periodic Table The vertical columns represent a series of elements with similar chemical and physical properties. The column are called families and each family has a specific name.

Examples of Some Families on the Periodic Table

Chemical Properties Very Reactive Good conductor of heat Good conductor of electricity Can explode if exposed to water Low melting and boiling temperature Low density Physical Properties All solid at room temperature Malleable Ductile Silvery coloured Lustrous Lithium Potassium Sodium

Chemical Properties Very reactive (less so than Alkalis) Good conductor of heat Good conductor of electricity Physical Properties Harder and Denser than Alkalis Lustrous Silvery-white colour All solid at room temperature Magnesium Beryllium Calcium

Chemical Properties High melting and boiling point High conductivity Less reactive than Alkali and Alkaline Metals Good conductor of heat Good conductor of electricity Physical Properties Very hard Malleable Ductile Lustrous Most are solid at room temperature Titanium Mercury

Chemical Properties Better conductor than non- metals but worse than metals Better conductors at high temperatures Polonium is radioactive Physical Properties Shiny or Dull Malleable Ductile Solid at room temperature Contains properties of both metals and non-metals Gives electrons to non-metals and takes electrons from metals. Arsenic Silicon Germanium

Chemical Properties Very reactive High ability to oxidize Fluorine and Chlorine are poisonous Bromine is toxic Astatine is radioactive Fluorine is the most reactive element Physical Properties Fluorine is a pale yellow gas Chlorine is a pale green gas Bromine is a brown liquid Iodine is a lustrous black solid Astatine is a solid BromineFluorineChlorine

Chemical Properties Almost completely non- reactive Low boiling point Helium has lowest boiling point of any substance Radon is radioactive Physical Properties All gases at room temperature XenonArgonHelium

Metals and Nonmetals Elements on the Periodic Table can be divided into metals and nonmetals. Metals are found on the left side of the zigzag line. Nonmetals are found on the right side of the zigzag line.

Metalloids Elements that touch either side of the zigzag line have some metal properties and some nonmetal properties. These are called metalloids.

Properties of Metals, Nonmetals, and Metalloids

By the mid 1800’s, several scientists were trying to sort the known elements according to atomic mass. Dmitri Mendeleev made a card for each known element with the following information: atomic mass, density, colour, melting point, and boiling point. He pinned all the cards to the wall in order of increasing atomic number. He then started moving the cards around and looking for patterns in their properties.

Mendeleev played cards for several months, arranging vertical and horizontal lines. He found that properties of elements repeated in periodic intervals (the first, the eighth and the fifteenth elements behaved similarly so they became a family). His pattern became known as the periodic table. Not all the elements had been discovered, but Mendeleev left gaps where he thought elements yet to be discovered should go. He correctly predicted properties of unknown elements.

Over the years, Mendeleev’s basic periodic table has become the foundation of modern chemistry.

A new Basis for the Periodic Table Mendeleev constructed his periodic table using chemical properties and atomic mass. Sometime though, the two conflicted and he had to chose between the two – and he chose property over atomic mass. Henry Moseley worked with Rutherford and discovered that the pattern of the periodic table fit together better when atomic number (number of protons) was used.

Mendeleev’s Periodic Table

Moseley’s Periodic Table

Alkaline Earth Metals Transition Metalloids Halogens Noble Gases Alkali METAL NON METAL